The 23-year-old has spent the last two seasons at Kings Langley, who were relegated to Division One Central at the end of last season.
The defender has been a target for Ginnelly for some time.
Lafleur had moved to Kings in October 2021.
He joined Gosport Borough during the 2018/19 season having started his career in the Watford youth set-up before joining Luton Town.
After his release by the Hatters in 2016, he moved to National League side Wealdstone, during which time he enjoyed loan spells at Harrow Borough, Chalfont St Peter and Edgware Town.
He then signed for Salisbury from Gosport in September 2019.
He moved to then-Southern Division One South outfit Moneyfields in July 2020 and then to Southern Premier Division South side Beaconsfield Town in the summer of 2021 and then onto Southern Premier Division Central outfit Kings Langley in October 2021.
Ginnelly told his club’s website: "We are absolutely delighted to finally get this deal done. Andy Danylyszyn and I had a meeting with Alex six months ago when we were unsure whether Jaden Charles would recover from his injuries. But we decided to wait for Jaden! Now, we've finally decided to make competition for places in the number 3 shirt our priority.
“Alex played against us a couple of times last season and both times he caught our eye. After having a few chats with the player from Kings Langley, we've decided to bring him on board.
“He's got a great delivery and bombs up and down the flanks, which will suit our style of play this season. He's also got the odd goal in his locker."
Ginnelly also revealed that midfielder Isaiah Osbourne had committed to Boro for 2023/24.
The experienced 35-year-old signed for club Nuneaton in October 2019.
Birmingham-born, he started his career with Aston Villa, making 19 Premier League appearances for the Villans and also featuring 4 times in the UEFA Cup.
He enjoyed loan spells with Nottingham Forest, Middlesbrough and Sheffield Wednesday before signing for Hibernian in August 2011.
After a season in Scotland, he spent two years at Blackpool and a year with Scunthorpe prior to moving to the Banks’s Stadium.
Injured for the 2015/16 season, he became an important player the following campaign and scored his only Walsall goal in a 1-1 draw with Bradford City in December 2016.
He joined Forest Green Rovers in September 2017 and was a near ever-present as Rovers retained their EFL status in 2017/18.
The former England under-16 international re-joined the Saddlers in August 2018 and made 32 appearances and scored 3 goals in 2018/19.
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